1. Field of the Invention
The present invention relates to a method for controlling a variable capacity compressor of an air conditioner, and more particularly, to a method for controlling a variable capacity compressor of an air conditioner, which can improve convergence and response properties of temperature by changing a control duty change rate, namely, the maximum value in a slew rate, according to a size of the control duty or a change in an air conditioning environment.
2. Background Art
In general, a variable capacity compressor for an air conditioner uses a pressure control valve to adjust a refrigerant discharge volume, but may adopt an ECV (Electronic Control Valve) using electric power instead of the pressure control valve of a mechanical structure. A variable capacity compressor adopting the ECV determines the refrigerant discharge volume of the compressor according to an inclination of a swash plate since the inclination of the swash plate is changed by the duty of the ECV. So, a refrigerant volume supplied to an evaporator is changed according to the duty of the ECV, and it means that the duty of the ECV is the main factor to determine evaporator temperature. The duty of the ECV is a value to indicate a time period, while the ECV is turned on, into percentage. Therefore, the refrigerant discharge volume of the compressor by time is increased when the duty is high, but is decreased when the duty is low.
As shown in FIG. 1, the air conditioner adopting the variable capacity compressor generally includes: an air conditioning case 210; an blower 220 mounted on an inlet side of the air conditioning case 210; an evaporator 200 mounted inside the air conditioning case 210 for cooling air using refrigerant discharged from a compressor 100; a heater core 230 mounted inside the air conditioning case 210 for receiving cooling water heated by an engine (E); a temperature control door 240 for controlling an opening and closing level of a cold air passageway and a hot air passageway of air passing through the evaporator 200; the compressor 100 for compressing and discharging refrigerant returned from the evaporator 200; a condenser 170 for condensing and discharging refrigerant supplied from the compressor 100; a receiver dryer 180 for gas-liquid separating refrigerant supplied from the condenser 170; and an expansion valve 190 for throttling refrigerant supplied from the receiver dryer 180 and sending it to the evaporator 200.
In the drawing, the unexplained reference numerals 212, 214 and 216 designate vents, and 212d, 214d and 216d designate doors for controlling the opening and closing amount of each of the vents 212, 214 and 216.
Meanwhile, a control unit 300 controls driving output of devices such as an electromagnetic clutch 146 for intermittently transmitting driving power of the engine (E) to the compressor 100, an ECV 160 for controlling a discharge volume of the compressor 100 by adjusting an inclination angle of the swash plate 144, and an actuator 310 for controlling the opening and closing level of the temperature control door 240. That is, the control unit 300 applies or interrupts electricity to or from the electromagnetic clutch 146, controls output voltage to the actuator 310 in such a way that the temperature control door 240 turns round toward a flow channel directing to the heater core 230 or a flow channel going round the heater core 230, and controls the duty of the ECV 160, namely, a time period while the ECV 160 is turned on, to increase and decrease the discharge volume of the compressor 100 by changing the inclination angle of the swash plate 144 against a driving shaft.
The unexplained reference numeral 320 designates an evaporator temperature sensor, 330 designates an outdoor temperature sensor, 340 designates an indoor temperature sensor, 350 designates a solar radiation sensor, 360 designates a cooling water temperature sensor. Sensing signals sensed by the above sensors are inputted to the control unit 300, and temperature set by a user, blower voltage, and so on are inputted to the control unit 300.
A target evaporator temperature is calculated by the set temperature of a car inputted by the user, the indoor temperature, the outdoor temperature and a solar radiation sensed and inputted from the sensors 330, 340 and 350 mounted at predetermined positions of the car. When the target evaporator temperature is calculated, a target duty of the ECV is calculated by evaporator temperature measured by the evaporator temperature sensor 320 and the target evaporator temperature.
When the target duty is calculated, the duty is changed from the current duty to the target duty by a predetermined slew rate, and in this instance, the slew rate is set not to exceed a basic slew rate (S0). Here, the slew rate means a change rate of the duty.
The basic slew rate (S0) is determined as a value to prevent hunting of the compressor, namely, a bump generated due to a sudden change of an introduced refrigerant volume of the compressor, and to minimize a pulsation of a refrigerant flow even though the introduced refrigerant volume of the compressor is changed.
According to a conventional compressor controlling method, the target duty is calculated by using the real evaporator temperature measured by the evaporator temperature sensor, the duty controlling the ECV, and the target evaporator temperature as a variable, and the calculated duty controls the ECV of the compressor. After the control of the ECV, the evaporator temperature is measured again, and the above process for calculating the target duty is repeated.
Even though the user suddenly manipulates a blower switch or changes the set temperature, the conventional compressor controlling method is deteriorated in convergence and response properties of the evaporator temperature since the duty change rate does not exceed the basic slew rate.
In other words, the conventional compressor controlling method controls in such a way that the duty change rate of the ECV 160, namely, the slew rate, cannot exceed the basic slew rate (S0) without regard to changes of the outside conditions. So, since the ECV duty is changed slowly even though the environment is suddenly changed, there occurs excessive overshoot or undershoot in evaporator temperature till the duty reaches the target duty, and thereby, it takes much time that the evaporator temperature reaches a stabilized state. Therefore, the conventional compressor controlling method has a problem in that convergence of the evaporator temperature and response properties to the user's manipulation of the air conditioner are deteriorated.